Reciprocating engines are common throughout the world and typically use a crank mechanism to convert reciprocating motion into rotary motion to drive a machine such as a vehicle. Due to the reciprocating nature of such engines, energy is lost during motion which reduces the efficiency of the engine and causes imbalances which result in wear of the components, unavoidable vibration of components and excessive noise.
There have been a number of attempts at addressing these issues. For example: rotary engines, orbital engines, split cycle engines, cam engines, axial engines, barrel engines—all representing engines whereby the crankshaft has been replaced by some other mechanism to convert reciprocating motion to rotational motion where many of the problems associated with the inherently out-of-balance crankshaft are alleviated to some extent.
Such engines can drive machines which include blades or rotors or the like at the end of a drive shaft to propel the machine (for example, a boat, plane, submarine, helicopter or the like). Especially in military machines, co-axial rotors have been utilized to turn a pair of rotors or propellers in opposite directions but are mounted on a single shaft with the same axis of rotation except for contra-rotating devices where the rotors or propellers are rotating on separate shafts on separate axes in opposite directions. Either configuration requires a gearbox of some description to convert a single shaft operation to two counter-rotating or coaxial shafts. A planetary gearset or similar gearbox is employed to convert the rotation of the drive shaft from the engine to a co-axial or counter-rotating shaft arrangement to drive the co-axial or counter-rotating propellers or rotors. Such systems are found in marine craft, for example. The two propellers or rotors are arranged one behind the other and the power is transferred from the engine via the gear transmission. There is a reduction in rotational flow providing a maximum amount of air or water uniformly through the propellers or rotors providing higher performance and less energy loss. Such systems also reduce or eliminate the amount of torque created by existing single propeller and rotor systems. However, these engines and associated transmission systems are typically expensive, mechanically complex, weigh more, cost more to maintain, are noisy and are prone to failure. For example, in a co-axial helicopter, the gearbox and rotor hub are extremely complicated with many linkages, plates and other parts that can fail due to the need to drive two rotor disks in opposite directions simultaneously.
It was suggested in AU 629,238 (the contents of which are incorporated herein by reference) engine complexity could be reduced by providing a crankless reciprocating engine. Such an engine could comprise at least one cylinder, two opposed pistons arranged to reciprocate in opposite directions along the longitudinal axis of each cylinder, the pistons defining a common combustion chamber therebetween, a main shaft disposed parallel to, and spaced from, the longitudinal axis of each cylinder, and two axially spaced, endless, substantially sinusoidal tracks carried by the main shaft for rotation therewith, said tracks being interconnected with said pistons so that reciprocation of the pistons imparts rotary motion to the main shaft. The engine further comprises a small charge and ignition chamber in communication with the common combustion chamber, means to admit fuel into the charge and ignition chamber to form a fuel rich charge therein and to form with air in the common combustion chamber a fuel lean charge therein. An ignition device is located in the charge and ignition chamber for ignition of the fuel rich charge therein.
However, with the above proposed engine there is still a need to resolve the problems associated with spinning two shafts concentrically in opposite directions on the same axis and problems with wear and complexity. Also, a gear box is required to convert the power and torque being delivered from a single shaft engine as discussed above to co-axial power.
Accordingly, there is a need to provide an engine which delivers full power and torque at the required RPM of the machine to concentric, coaxial shafts without the need for a gearbox.